4 years is pretty good, maybe you could post a graph? I know that a lot of people here are young, so they've started to have weight problems only recently, and hence haven't been recording their weight. I use Excel, but really, any program that is easy to use (Excel, Works) is fine. If someone is considering buying some software, I'd go for either Office 97 or later, or Microsoft Works 98 or later. For the average user, spreadsheets haven't really evolved in the last 10 years or so.

My only tip is to have a row for every day (so there are 365 rows in a year), rather than per week or per reading. You can Fill Down or set that cell to be equal to the cell above it (and Fill Down this as well), so you don't actually need to weigh yourself every day.

The reason for this is you're bound to have periods where you weigh daily, and bound to have periods where you don't. If you have mixed periods, averaging over x-days is screwed up and also you'll have to use x-y plot instead of others. Converting from mixed periods to daily is the sort of thing you don't want to do, I did my brothers data last night and it took about 4 hours, I think it took me about double that when I did my data nearly 10 years ago.